On 10/20/25 12:03, Song Liu wrote:
> On Mon, Oct 20, 2025 at 7:56 AM Andrey Grodzovsky
> <andrey.grodzovsky@crowdstrike.com> wrote:
> [...]
>>> If you build the kernel from source code, there are some samples in
>>> samples/livepatch that you can use for testing. PS: You need to enable
>>>
>>>     CONFIG_SAMPLE_LIVEPATCH=m
>>>
>>> I hope this helps.
>> Thanks Song, working on repro, kernel rebuilt, test module is loading
>> but, bpftrace is refusing to attach now to fentries/fexits claiming the
>> costum kernel is not supporting it. It did
>> attach in the case of stock AWS kernel i copied the .config from. So
>> just trying to figure out now if some Kcofnig flags are missing or
>> different . Let me know in case you manage to confirm yourself in the
>> meanwhile the fix works for
>> you.
> Yes, it worked in my tests.
>
> [root@(none) /]# kpatch load linux/samples/livepatch/livepatch-sample.ko
> loading patch module: linux/samples/livepatch/livepatch-sample.ko
> [root@(none) /]# bpftrace.real -e 'fexit:cmdline_proc_show
> {printf("fexit\n");}' &
> [1] 388
> [root@(none) /]# Attached 1 probe
> [root@(none) /]# bpftrace.real -e 'fentry:cmdline_proc_show
> {printf("fentry\n");}' &
> [2] 397
> [root@(none) /]# Attached 1 probe
>
> [root@(none) /]# cat /proc/cmdline
> this has been live patched
> fentry
> fexit
>
> Thanks,
> Song
>

Verified the failures I observe when trying to attach with BPF trace are 
only in presence of patch you provided.
Please see attached dmesg for failures. Initial warning on boot. 
Subsequebt warnings and errors at the point i try to run
sudo bpftrace -e "fexit:cmdline_proc_show { printf(\"fexit hit\\n\"); 
exit(); }"

sudo: unable to resolve host ip-10-10-115-238: Temporary failure in name 
resolution
stdin:1:1-25: ERROR: kfunc/kretfunc not available for your kernel version.

ubuntu@ip-10-10-115-238:~/linux-6.8.1$ sudo cat 
/sys/kernel/debug/tracing/available_filter_functions | grep 
cmdline_proc_show
sudo: unable to resolve host ip-10-10-115-238: Temporary failure in name 
resolution
cat: /sys/kernel/debug/tracing/available_filter_functions: No such device

After reboot and before trying to attacg with bpftrace, 
/sys/kernel/debug/tracing/available_filter_functions is available and 
shows all function.

Using stable kernel from 
https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.8.1.tar.gz for build.
FTRACE related KCONFIGs bellow

ubuntu@ip-10-10-115-238:~$ cat /boot/config-6.8.1 | grep TRACE
CONFIG_TASKS_TRACE_RCU=y
CONFIG_SYSCTL_EXCEPTION_TRACE=y
CONFIG_TRACEPOINTS=y
CONFIG_STACKTRACE_SUPPORT=y
CONFIG_PM_TRACE=y
CONFIG_PM_TRACE_RTC=y
CONFIG_KPROBES_ON_FTRACE=y
CONFIG_HAVE_KPROBES_ON_FTRACE=y
CONFIG_ARCH_CORRECT_STACKTRACE_ON_KRETPROBE=y
CONFIG_TRACE_IRQFLAGS_SUPPORT=y
CONFIG_TRACE_IRQFLAGS_NMI_SUPPORT=y
CONFIG_HAVE_ARCH_TRACEHOOK=y
CONFIG_HAVE_RELIABLE_STACKTRACE=y
CONFIG_NETFILTER_XT_TARGET_TRACE=m
# CONFIG_DMA_FENCE_TRACE is not set
CONFIG_SCSI_IPR_TRACE=y
# CONFIG_ATH5K_TRACER is not set
# CONFIG_DRM_I915_LOW_LEVEL_TRACEPOINTS is not set
CONFIG_STM_SOURCE_FTRACE=m
# CONFIG_PSTORE_FTRACE is not set
# CONFIG_STACKTRACE_BUILD_ID is not set
CONFIG_STACKTRACE=y
# CONFIG_RCU_TRACE is not set
CONFIG_USER_STACKTRACE_SUPPORT=y
CONFIG_NOP_TRACER=y
CONFIG_HAVE_FUNCTION_TRACER=y
CONFIG_HAVE_FUNCTION_GRAPH_TRACER=y
CONFIG_HAVE_DYNAMIC_FTRACE=y
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_REGS=y
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=y
CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS=y
CONFIG_HAVE_DYNAMIC_FTRACE_NO_PATCHABLE=y
CONFIG_HAVE_FTRACE_MCOUNT_RECORD=y
CONFIG_HAVE_SYSCALL_TRACEPOINTS=y
CONFIG_TRACER_MAX_TRACE=y
CONFIG_TRACE_CLOCK=y
CONFIG_CONTEXT_SWITCH_TRACER=y
CONFIG_GENERIC_TRACER=y
CONFIG_FTRACE=y
CONFIG_FUNCTION_TRACER=y
CONFIG_FUNCTION_GRAPH_TRACER=y
CONFIG_DYNAMIC_FTRACE=y
CONFIG_DYNAMIC_FTRACE_WITH_REGS=y
CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS=y
CONFIG_DYNAMIC_FTRACE_WITH_ARGS=y
CONFIG_STACK_TRACER=y
# CONFIG_IRQSOFF_TRACER is not set
CONFIG_SCHED_TRACER=y
CONFIG_HWLAT_TRACER=y
CONFIG_OSNOISE_TRACER=y
CONFIG_TIMERLAT_TRACER=y
CONFIG_MMIOTRACE=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_TRACER_SNAPSHOT=y
# CONFIG_TRACER_SNAPSHOT_PER_CPU_SWAP is not set
CONFIG_BLK_DEV_IO_TRACE=y
# CONFIG_KPROBE_EVENTS_ON_NOTRACE is not set
CONFIG_FTRACE_MCOUNT_RECORD=y
CONFIG_FTRACE_MCOUNT_USE_CC=y
CONFIG_TRACE_EVENT_INJECT=y
# CONFIG_TRACEPOINT_BENCHMARK is not set
# CONFIG_TRACE_EVAL_MAP_FILE is not set
# CONFIG_FTRACE_RECORD_RECURSION is not set
# CONFIG_FTRACE_STARTUP_TEST is not set
CONFIG_FTRACE_SORT_STARTUP_TEST=y
# CONFIG_MMIOTRACE_TEST is not set
# CONFIG_SAMPLE_TRACE_EVENTS is not set
# CONFIG_SAMPLE_TRACE_CUSTOM_EVENTS is not set
CONFIG_SAMPLE_TRACE_PRINTK=m
CONFIG_SAMPLE_FTRACE_DIRECT=m
# CONFIG_SAMPLE_FTRACE_DIRECT_MULTI is not set
# CONFIG_SAMPLE_FTRACE_OPS is not set
CONFIG_SAMPLE_TRACE_ARRAY=m
CONFIG_HAVE_SAMPLE_FTRACE_DIRECT=y
CONFIG_HAVE_SAMPLE_FTRACE_DIRECT_MULTI=y
CONFIG_HAVE_MMIOTRACE_SUPPORT=y
CONFIG_CC_HAS_SANCOV_TRACE_PC=y
# CONFIG_BACKTRACE_SELF_TEST is not set


Andrey